1. Field of the Invention
The present invention relates to an apparatus for measuring the velocity of propagation of a pulse wave which is propagated through an artery of a living subject.
2. Related Art Statement
The blood pressure, degree of arterial sclerosis, peripheral resistance, etc. of a living subject can be estimated based on the velocity of propagation of a pulse wave which is propagated through an artery of the subject. There is known a pulse-wave propagation velocity measuring apparatus including a pair of pulse-wave sensors which are put on different locations on the skin of a living subject to press different portions of an artery of the subject via the skin and detect respective pulse waves from the artery. The measuring apparatus determines a pulse-wave propagation velocity based on the phase difference of the two pulse waves detected through the two sensors. The measuring apparatus is disclosed in, e.g., Unexamined Japanese Patent Application laid open for inspection purposes under Publication No. 60(1985)-220037.
The prior measuring apparatus measures the pulse-wave propagation velocity through the pulse-wave sensors being pressed against two portions of a superficial artery, such as carotid artery, radial artery, or dorsal pedal artery, that is adjacent to the skin of the subject. In this case, however, the time difference between the time of occurrence or detection of a heartbeat-synchronous pulse of one of the two pulses waves and the time of occurrence or detection of a corresponding heartbeat-synchronous pulse of the other pulse wave is small, because the length or distance between the two portions of the superficial artery is short. Thus, the time difference may not be relied upon for providing a very accurate pulse-wave propagation velocity.